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'[ot]: using a pic in an automotive application'
2001\03\05@170237 by rad0

picon face
I remember seeing talk about people using a pic
on a 12v automobile system.

What's the best way to isolate it from the high amp
perhaps spikey car system?

The discussionwas lost from my archives, so what
did everyone agree upon for powering the pic.

thanks



btw, my application here is to build a sensing system that
turns on trailer lights when the coresponding auto lights
are on.

I had in mind to somehow 'sense' when the tail lights, blinker,
stop lights were on then turn on the corresponding light on
the trailer.  I though I could just use a direct wire from the battery
to connect to a 'system' bus, then use solid state relays to
connect up the coresponding light.

Is this totally out to lunch?  or could this reasonably be done?

One, I want to totally isolate it from the auto-tow-vehicle as much
as possible.  And I'm not sure how to 'sense' when a particular
light is on.  I thought I could perhaps use a giant diode and some
sort of isolation to bring it down to ttl so I can connect it to my
pic.  Perhaps an optical isolator, is this practical?

Two, having a direct to battery buss and slamming lights on and off
of it might be a problem.  Is it?  Will this cause gross surges that
ought not to be done?  If so, how do you 'isolate' or buffer this?

thanks

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2001\03\05@174640 by Lawrence Lile

flavicon
face
As I remember, automotive power is a pretty rough environment.  The normal
fault conditions on an automotive power system include reverse polarity, and
two-battery jump starts ( >24V +++).  The system runs around 13 to 17 volts
normally, with plenty of RFI from the ignition, but may dip below 10V.  Oh,
yeah, and it's got to run at nice high temperatures in the hot sun over
black pavement as well as in January in Minnesota.  You power supply has to
take all these lickin's and keep on tickin'.  One of the worst environnments
outside of downhole applications that I can think of.

-- Lawrence Lile



{Original Message removed}

2001\03\05@180137 by Tony Nixon

flavicon
picon face
rad0 wrote:
>
> I remember seeing talk about people using a pic
> on a 12v automobile system.
>
> What's the best way to isolate it from the high amp
> perhaps spikey car system?
>
> The discussionwas lost from my archives, so what
> did everyone agree upon for powering the pic.
>

There is a power supply circuit here. It is simple, but after years of
use on 1000's of cars it appears to work ok. I doubt it would protect
the PIC in a 'load dump' situation.

http://www.picnpoke.com/projects/ignition.html

Keep high power ground returns seperate from low power PIC circuits.
I've had situations where a connection comes loose, and the ground tries
to route itself through the PCB traces which tend to vaporise. The PIC
still worked though.

High power GND ____      _____ Low power ground
                  \    /
                   \  /
                    \/
                   ----
                   ////


> Is this totally out to lunch?  or could this reasonably be done?

Only if you had a 'light' lunch ;-}

> One, I want to totally isolate it from the auto-tow-vehicle as much
> as possible.  And I'm not sure how to 'sense' when a particular
> light is on.  I thought I could perhaps use a giant diode and some
> sort of isolation to bring it down to ttl so I can connect it to my
> pic.  Perhaps an optical isolator, is this practical?

Perhaps a standard trailer plug and use the connections to drive opto
isolators in the trailer circuit. I don't know if it is practical or
possible to isolate the trailor earth from the vehicle earth.

> Two, having a direct to battery buss and slamming lights on and off
> of it might be a problem.  Is it?  Will this cause gross surges that
> ought not to be done?  If so, how do you 'isolate' or buffer this?

BD681 NPN transistors should be able to drive the 12V bulbs direct from
a PIC pin (via base resistors). Bulbs are not highly inductive, so I
doubt you will have any problems. Keep the circuit out of the heat
though.

--
Best regards

Tony

mICro's
http://www.picnpoke.com
spam_OUTsalesTakeThisOuTspampicnpoke.com

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2001\03\05@181936 by rad0

picon face
thanks for the suggestions so far,

the reason I want to do this is to

TOTALLY isolate the trailer from the tow-vehicle
as far as possible...

I want the tow vehicle to feel nothing, and only give
a ttl indication that a light is on...

thanks


{Original Message removed}

2001\03\05@225425 by Sean H. Breheny

face picon face
Hi Lawrence,

Don't forget about load drop: your circuit should be tolerant of high
voltage spikes in case the battery connector is loose and you suddenly have
the inductance of the alternator (or other components) trying to force a
huge current (which WAS charging the battery before the connection was
interrupted) through your circuit.

Sean

At 04:47 PM 3/5/01 -0600, Lawrence Lile wrote:
{Quote hidden}

>{Original Message removed}

2001\03\06@032141 by Roman Black

flavicon
face
rad0 wrote:
>
> thanks for the suggestions so far,
>
> the reason I want to do this is to
>
> TOTALLY isolate the trailer from the tow-vehicle
> as far as possible...
>
> I want the tow vehicle to feel nothing, and only give
> a ttl indication that a light is on...
>
> thanks


You know you can buy solid state trailer light
driver boxes for about $7 US?? Some of the
motorbike guys use them for turn signal
drivers. I think Wal-mart was mentioned as
the supplier. :o)
-Roman

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2001\03\06@081651 by rad0

picon face
I want to build something that cannot fail...

and when it does, it tells you what's wrong...

after all, when you're out on the road and your 7$
box fails, and it's raining, and cold, and the cop wants
to give you a ticket, etc etc

these boxes simply don't work, I know they exist...


{Original Message removed}

2001\03\06@082315 by Roman Black

flavicon
face
rad0 wrote:
>
> I want to build something that cannot fail...
>
> and when it does, it tells you what's wrong...
>
> after all, when you're out on the road and your 7$
> box fails, and it's raining, and cold, and the cop wants
> to give you a ticket, etc etc
>
> these boxes simply don't work, I know they exist...


Ok, that's fine. I was worried you might be working
hard on a product that is already being mass produced
in Asia and sold cheap in supermarkets. That would
hurt!:o)

To make good automotive device you probably
need to decide what is your "brains" circuit and
what is your "power" circuit. Then you will need
different approaches with how you handle power
protection with both circuits, and how they connect
to each other.
-Roman

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2001\03\06@092918 by rad0

picon face
Alright,

Thanks for the important tips.

This is just a hobby thing.

But it stems from failure of the new comercial product
that I just installed and didn't last more than 60 miles
or half an hour...

I was thinking about separating the power circuit from the
brain circuit as you mentioned.  But I'm not sure how to go
about this.

I had thought that I could build a main bus, direct from
the battery, that I could use for powering the actual lights
on the trailer using relays of some type.

As far as the brains power, I was going to connect it's
power supply to this 'bus' also, but I wanted to isolate
it somehow, from the so-called harsh environment.

I have seen dc - to - dc power supplies, are these
suitable, or hearty enough to get my 5vdc supply
and protect from all the suposed spikes.  I also,
want to protect the vehicle's onboard computer
systems...

Thanks
Roman and all...

{Original Message removed}

2001\03\06@103147 by Mike Mansheim

flavicon
face
> But it stems from failure of the new comercial product
> that I just installed and didn't last more than 60 miles
> or half an hour...

I don't know where you're from, but I'm jealous:  120 mph
is severely frowned upon here.

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2001\03\06@104633 by rad0

picon face
I said 'or'

I didn't notice exactly when the lights went
out during day light...


----- Original Message -----
From: "Mike Mansheim" <EraseMEMichael_J_Mansheimspam_OUTspamTakeThisOuTGRACO.COM>
To: <PICLISTspamspam_OUTMITVMA.MIT.EDU>
Sent: Tuesday, March 06, 2001 9:27 AM
Subject: Re: [ot]: using a pic in an automotive application


{Quote hidden}

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2001\03\06@121246 by Dwayne Reid

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face
At 08:30 AM 3/6/01 -0600, rad0 wrote:
>Alright,
>
>Thanks for the important tips.
>
>This is just a hobby thing.
>
>But it stems from failure of the new comercial product
>that I just installed and didn't last more than 60 miles
>or half an hour...

Are you sure that is the failure of the box responsible for the traffic
ticket?
60 miles in half an hour.

<grin>

Just couldn't resist!

dwayne



Dwayne Reid   <RemoveMEdwaynerTakeThisOuTspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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Celebrating 17 years of Engineering Innovation (1984 - 2001)

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2001\03\07@053144 by Spehro Pefhany

picon face
At 09:24 AM 3/6/01 +1100, you wrote:
>
>There is a power supply circuit here. It is simple, but after years of
>use on 1000's of cars it appears to work ok. I doubt it would protect
>the PIC in a 'load dump' situation.
>
>http://www.picnpoke.com/projects/ignition.html

(other good stuff snipped)

This one doesn't look too bad. I'd replace the Zener diode with a TVS,
for example a P6KE20 type. It costs a bit more than the Zener (well,
about 3 x) but is rated to protect the circuit. Not much different
size.

(Load dump is a brief transient up to about +160VDC followed by a long,
slow ramp down from about +40V to ~14V (normal) over about 0.1 second.)

Best regards,


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2001\03\07@170402 by Peter L. Peres

picon face
Umm, look, the simplest trailer circuit I know of consists of two 250A
diodes. One is in series with the + from the car to the trailer and does
not allow current from the trailer into the car, and the second is in the
trailer supplying power from the trailer battery to the trailer only. The
trailer will run up to 1V lower than normal at normal currents but this is
not a problem normally. How you charge the trailer battery is another
matter. This diode thing is relatively bombproof.

Now, if you want to improve this, in a failsafe way (haha), then you can
add current and voltage sensors across each diode and place a big VFET in
parallel with each, such that it turns on and 'helps' the diode when the
current tries to flow in the desired direction.

The next improvement implies a relay that separates the car battery from
the trailer if the voltage decreases below a certain level (that will
allow you to start the car if you want to etc).

The same circuit can be added in the trailer to protect the trailer
battery but it should have a warning device that warns the people in the
trailer early about the oncoming blackout.

Last, a charger circuit can be built that detects when current is
available from the car battery and disconnects the trailer battery from
the trailer, and charges it using a small DC/DC converter.

Now, each of these units operates independently and can be built
separately. The probability that it will all blow up at once is very low
and you can probably have a very high degree of confidence in the system
if built 'right'.

hope this helps,

Peter

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